1. Field of the Invention
The present invention relates to a power supply circuit.
2. Description of Related Art
A power supply circuit illustrated in FIG. 19 uses an output circuit 910 including a serial circuit of a high side FET disposed on a high voltage side and a low side FET disposed on a low voltage side, so as to generate an output voltage Vo′ from an input voltage. In the power supply circuit illustrated in FIG. 19, each FET is controlled to turn on and off based on a feedback voltage VFB′ corresponding to the output voltage Vo′.
In this case, as illustrated in FIG. 20, the feedback voltage VFB′ is compared with each of voltages (VREF′+ΔV) and (VREF′−ΔV), and the FETs are controlled to turn on and off based on the comparison results so that the output voltage Vo′ can be stabilized to a desired voltage corresponding to the reference voltage VREF′.
Note that there are following technical documents related to the present invention: (1) JP-A-2009-219184, (2) JP-A-2012-156826, and (3) JP-A-2002-335145.
A load of a power supply circuit sometimes requires large current. For instance, when a signal processor configured to perform signal processing on data of a magnetic disk is a load of the power supply circuit, the signal processor requires large current particularly in reading and writing data. On the contrary, there are cases where the signal processor does not require large current. In view of this situation, it is considered to prepare two output circuits 910 illustrated in FIG. 19 to be connected in parallel. When small current is required, only one output circuit 910 is used to generate the output voltage Vo′ (hereinafter referred to as single driving). When large current is required, two output circuits 910 are driven in parallel to generate the output voltage Vo′. However, it is necessary to consider so that stable operation of the load is not disturbed when switching from the single driving to the parallel driving (for example, consideration for preventing a transient drop of the output voltage).
In addition, if a hysteresis voltage ΔV can be accurately generated in FIG. 20, an accuracy of the output voltage is improved (the output voltage Vo′ is identical to the desired voltage with high accuracy). The improvement of the output voltage accuracy also contributes to the stable operation of the load.